package client

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// Config is what a client remembers between runs, and every setting a user
// can change. The session token lives here; the KDBX master passwords never
// do, because the client never opens a database, it only moves bytes.
//
// The file is written with every field present, so editing it is the whole
// of the client's settings interface: the tray's "Open Config" opens it, and
// the tray picks up a saved change without restarting.
type Config struct {
	// ServerURL is the server's base URL, as a browser sees it.
	ServerURL string `json:"server_url"`
	// Username and Token are written by signing in, not by hand.
	Username string `json:"username"`
	Token    string `json:"token"`
	// DeviceLabel names this device in the server's session list.
	DeviceLabel string `json:"device_label"`
	// MirrorDir is where the databases appear as .kdbx files.
	MirrorDir string `json:"mirror_dir"`
	// PollSeconds is how often the mirror is rescanned for local saves.
	PollSeconds int `json:"poll_seconds"`
	// RequestTimeoutSeconds bounds one API call. The event stream is exempt.
	RequestTimeoutSeconds int `json:"request_timeout_seconds"`
	// CAFile is a PEM bundle trusted in addition to the system roots, for a
	// server behind a private certificate authority.
	CAFile string `json:"ca_file"`
	// LogFile is where the agent logs. Empty means standard error for
	// `keeporg run`, and keeporg.log beside this file for the tray.
	LogFile string `json:"log_file"`
	// Notifications turns the tray's desktop notifications on or off.
	Notifications bool `json:"notifications"`
	// AllowInsecureHTTP permits an http:// server_url that is not this
	// machine. Without TLS the password, the session token and every vault
	// cross the network readable and alterable by anyone on the path.
	AllowInsecureHTTP bool `json:"allow_insecure_http"`
}

// ErrNoConfig means the client has not been logged in yet.
var ErrNoConfig = errors.New("not logged in: run `keeporg login` first")

// DefaultConfigPath is the per-user configuration path on this platform.
func DefaultConfigPath() string {
	dir, err := os.UserConfigDir()
	if err != nil {
		return filepath.Join(".", ".keeporg", "config.json")
	}
	return filepath.Join(dir, "keeporg", "config.json")
}

// DefaultMirrorDir is where databases are mirrored unless told otherwise.
func DefaultMirrorDir() string {
	home, err := os.UserHomeDir()
	if err != nil {
		return "keeporg"
	}
	return filepath.Join(home, "KeepOrg")
}

// DefaultConfig is a configuration with every setting at its default and no
// server.
func DefaultConfig() *Config {
	label, err := os.Hostname()
	if err != nil || label == "" {
		label = "keeporg client"
	}
	return &Config{
		DeviceLabel:           label,
		MirrorDir:             DefaultMirrorDir(),
		PollSeconds:           2,
		RequestTimeoutSeconds: 60,
		Notifications:         true,
	}
}

// LoadConfig reads a configuration file. A setting the file leaves out keeps
// its default, so an older file reads the same as it always did.
func LoadConfig(path string) (*Config, error) {
	b, err := os.ReadFile(path)
	if os.IsNotExist(err) {
		return nil, ErrNoConfig
	}
	if err != nil {
		return nil, err
	}
	c := DefaultConfig()
	if err := json.Unmarshal(b, c); err != nil {
		return nil, fmt.Errorf("%s: %w", path, err)
	}
	def := DefaultConfig()
	if c.MirrorDir == "" {
		c.MirrorDir = def.MirrorDir
	}
	if c.DeviceLabel == "" {
		c.DeviceLabel = def.DeviceLabel
	}
	if c.PollSeconds <= 0 {
		c.PollSeconds = def.PollSeconds
	}
	if c.RequestTimeoutSeconds <= 0 {
		c.RequestTimeoutSeconds = def.RequestTimeoutSeconds
	}
	c.ServerURL = strings.TrimRight(c.ServerURL, "/")
	c.MirrorDir = expandHome(c.MirrorDir)
	c.CAFile = expandHome(c.CAFile)
	c.LogFile = expandHome(c.LogFile)
	return c, c.Validate()
}

// EnsureConfig returns the configuration at path, writing a default one
// first if there is none, so a user always has a complete file to edit.
func EnsureConfig(path string) (*Config, error) {
	c, err := LoadConfig(path)
	if !errors.Is(err, ErrNoConfig) {
		return c, err
	}
	c = DefaultConfig()
	return c, c.Save(path)
}

// Validate reports the first setting that cannot work.
func (c *Config) Validate() error {
	if c.ServerURL != "" {
		u, err := url.Parse(c.ServerURL)
		if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
			return fmt.Errorf("server_url %q must be an http:// or https:// URL", c.ServerURL)
		}
		if u.Scheme == "http" && !isLoopback(u.Hostname()) && !c.AllowInsecureHTTP {
			return fmt.Errorf("server_url %q is not encrypted; use https://, "+
				"or set allow_insecure_http if you really mean it", c.ServerURL)
		}
	}
	if c.CAFile != "" {
		if _, err := os.Stat(c.CAFile); err != nil {
			return fmt.Errorf("ca_file: %w", err)
		}
	}
	return nil
}

func isLoopback(host string) bool {
	if host == "localhost" {
		return true
	}
	ip := net.ParseIP(host)
	return ip != nil && ip.IsLoopback()
}

// CheckVerificationURL makes sure a page the server asks the client to open
// in a browser is on that server. A compromised server must not be able to
// make the desktop open whatever it likes — a file: URL, a network share
// that runs a program, another application's URL scheme.
func CheckVerificationURL(serverURL, raw string) error {
	srv, err := url.Parse(serverURL)
	if err != nil {
		return err
	}
	u, err := url.Parse(raw)
	if err != nil || u.Scheme != srv.Scheme || !strings.EqualFold(u.Host, srv.Host) ||
		u.User != nil || u.Path != strings.TrimRight(srv.Path, "/")+"/device" {
		return fmt.Errorf("the server asked to open %q, which is not its own approval page", raw)
	}
	return nil
}

// API returns a client for the configured server, signed in with the stored
// token when there is one.
func (c *Config) API() (*API, error) {
	api := NewAPI(c.ServerURL, c.Token)
	api.HTTP.Timeout = time.Duration(c.RequestTimeoutSeconds) * time.Second
	if c.CAFile == "" {
		return api, nil
	}
	pem, err := os.ReadFile(c.CAFile)
	if err != nil {
		return nil, fmt.Errorf("ca_file: %w", err)
	}
	pool, err := x509.SystemCertPool()
	if err != nil {
		pool = x509.NewCertPool()
	}
	if !pool.AppendCertsFromPEM(pem) {
		return nil, fmt.Errorf("ca_file %s holds no PEM certificates", c.CAFile)
	}
	tr := http.DefaultTransport.(*http.Transport).Clone()
	tr.TLSClientConfig = &tls.Config{RootCAs: pool, MinVersion: tls.VersionTLS12}
	api.HTTP.Transport = tr
	return api, nil
}

// Poll is PollSeconds as a duration.
func (c *Config) Poll() time.Duration { return time.Duration(c.PollSeconds) * time.Second }

// Save writes the configuration with owner-only permissions, since it holds
// a bearer token.
func (c *Config) Save(path string) error {
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return err
	}
	b, err := json.MarshalIndent(c, "", "  ")
	if err != nil {
		return err
	}
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, append(b, '\n'), 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, path)
}

// expandHome turns a leading ~ into the home directory, since the file is
// meant to be edited by hand.
func expandHome(p string) string {
	if p != "~" && !strings.HasPrefix(p, "~/") && !strings.HasPrefix(p, `~\`) {
		return p
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return p
	}
	return filepath.Join(home, p[1:])
}